Add automated testing

[pydsigner]

We should add a few tests for each function currently available through these bindings.

[mafr]

I have a few happy path tests that I can contribute. Still haven't figured out how to get the parser flags and the unused_symbols parameter to do anything different, though.

[mafr]

There are a few tests on this branch: https://github.com/mafr/python-lightningcss/tree/feature/add-tests

Let me know if you're interested, but I haven't looked into GitHub Actions to automate test execution yet.

[pydsigner]

Compare https://github.com/pydsigner/python-lightningcss/blob/master/.github/workflows/CI.yml with https://github.com/pydsigner/anchovy/blob/master/.github/workflows/python-cq.yml. I don't know that the linting/test coverage checks are needed but the basic pattern is there.

[mafr]

Thanks - that looks similar to what I use on Bitbucket.

How do you want to have this integrated? As another step in each job (install pytest, then run tests), or as a separate job that builds and runs the tests?

[pydsigner]

I don't think we need to run tests across the full matrix at this point. But we could use the wheel created in the build job too. So I think a separate job that waits for the linux build to finish and then uses one of the wheels for install?

[pydsigner]

Closed in #15.